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docs/patterns/mongoengine.rst
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David Lord
update flask-mongoengine link
13 май 2026, 17:37
13 май 2026, 17:371d49747
MongoDB with MongoEngine
========================

Using a document database like MongoDB is a common alternative to
relational SQL databases. This pattern shows how to use
`MongoEngine`_, a document mapper library, to integrate with MongoDB.

A running MongoDB server and `Flask-MongoEngine`_ are required. ::

    pip install flask-mongoengine

.. _MongoEngine: http://mongoengine.org
.. _Flask-MongoEngine: https://docs.mongoengine.org/projects/flask-mongoengine/en/latest/

Configuration
-------------

Basic setup can be done by defining ``MONGODB_SETTINGS`` on
``app.config`` and creating a ``MongoEngine`` instance. ::

    from flask import Flask
    from flask_mongoengine import MongoEngine

    app = Flask(__name__)
    app.config['MONGODB_SETTINGS'] = {
        "db": "myapp",
    }
    db = MongoEngine(app)


Mapping Documents
-----------------

To declare a model that represents a Mongo document, create a class that
inherits from ``Document`` and declare each of the fields. ::

    import mongoengine as me

    class Movie(me.Document):
        title = me.StringField(required=True)
        year = me.IntField()
        rated = me.StringField()
        director = me.StringField()
        actors = me.ListField()

If the document has nested fields, use ``EmbeddedDocument`` to
defined the fields of the embedded document and
``EmbeddedDocumentField`` to declare it on the parent document. ::

    class Imdb(me.EmbeddedDocument):
        imdb_id = me.StringField()
        rating = me.DecimalField()
        votes = me.IntField()

    class Movie(me.Document):
        ...
        imdb = me.EmbeddedDocumentField(Imdb)


Creating Data
-------------

Instantiate your document class with keyword arguments for the fields.
You can also assign values to the field attributes after instantiation.
Then call ``doc.save()``. ::

    bttf = Movie(title="Back To The Future", year=1985)
    bttf.actors = [
        "Michael J. Fox",
        "Christopher Lloyd"
    ]
    bttf.imdb = Imdb(imdb_id="tt0088763", rating=8.5)
    bttf.save()


Queries
-------

Use the class ``objects`` attribute to make queries. A keyword argument
looks for an equal value on the field. ::

    bttf = Movie.objects(title="Back To The Future").get_or_404()

Query operators may be used by concatenating them with the field name
using a double-underscore. ``objects``, and queries returned by
calling it, are iterable. ::

    some_theron_movie = Movie.objects(actors__in=["Charlize Theron"]).first()

    for recents in Movie.objects(year__gte=2017):
        print(recents.title)


Documentation
-------------

There are many more ways to define and query documents with MongoEngine.
For more information, check out the `official documentation
<MongoEngine_>`_.

Flask-MongoEngine adds helpful utilities on top of MongoEngine. Check
out their `documentation <Flask-MongoEngine_>`_ as well.